Cutaneous vascular responses of the hands and feet to cooling, rewarming, and hypoxia in humans

Introduction - This study investigated skin vasomotor responses in the fingers and toes during cooling and rewarming with, and without, normobaric hypoxia.

Methods - Fourteen volunteers (8 males and 6 females) were exposed to gradual air cooling (mean ± SD -0.4 ± 0.1oC.min-1) followed by rewarming (+0.5 ± 0.1oC.min-1) whilst breathing normoxic air (FIO2 0.21 at41 761 ± 3 mmHg) or hypoxic gas (FIO2 0.12, at 761 ± 3 mmHg equivalent to ~5000 m above sea level). Throughout the gradual cooling and rewarming phases rectal temperature was measured, and skin temperatures and laser Doppler skin blood flow were measured on the thumb, little finger, great and little toe pads.

Results - During gradual cooling, skin but not deep body temperature decreased. No differences in cutaneous vascular conductance (CVC) were found for the toes or thumb (P=0.169 great toe; P=0.289 little toe; thumb P=0.422). CVC was reduced in the little finger to a greater extent at the same mean skintemperatures (34.5oC to 33.5o C) in the hypoxic compared to normoxic conditions (P=0.047). The onset of vasoconstriction and release of vasoconstriction in the thumb and little finger occurred at higher mean skin temperatures in hypoxia compared to normoxia (P<0.05). The onset of vasoconstriction and release of vasoconstriction in the toes occurred at similar skin temperatures (P=0.181 and P=0.132, respectively).

Conclusion - The earlier vasoconstrictor response and later release of vasoconstriction in the finger during hypoxic conditions may result in a greater dose of cold to that digit, taking longer to rewarm following the release of vasoconstriction.